From:   Sergey Organov <sorganov@gmail.com>
To:     Ilpo =?utf-8?Q?J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
Cc:     linux-serial@vger.kernel.org, Fabio Estevam <festevam@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Richard Genoud <richard.genoud@gmail.com>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>,
        Tim Harvey <tharvey@gateworks.com>,
        Tomasz =?utf-8?Q?Mo=C5=84?= <tomasz.mon@camlingroup.com>,
        linux-arm-kernel@lists.infradead.org,
        NXP Linux Team <linux-imx@nxp.com>,
        Pengutronix Kernel Team <kernel@pengutronix.de>
Subject: Re: [PATCH 6/8] serial: imx: stop using USR2 in FIFO reading loop
References: <87bko4e65y.fsf@osv.gnss.ru>
        <20230113184334.287130-1-sorganov@gmail.com>
        <20230113184334.287130-7-sorganov@gmail.com>
        <3c9ab74b-ff90-8371-75cd-1d2f7abb388d@linux.intel.com>
Date:   Tue, 17 Jan 2023 16:30:26 +0300
In-Reply-To: <3c9ab74b-ff90-8371-75cd-1d2f7abb388d@linux.intel.com> ("Ilpo
        =?utf-8?Q?J=C3=A4rvinen=22's?= message of "Mon, 16 Jan 2023 12:54:19 +0200
 (EET)")
Message-ID: <874jsp47bh.fsf@osv.gnss.ru>
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Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> writes:

> On Fri, 13 Jan 2023, Sergey Organov wrote:
>
>> The chip provides all the needed bits in the URXD0 register that we read
>> anyway for data, so get rid of reading USR2 and use only URXD0 bits
>> instead.
>> 
>> Signed-off-by: Sergey Organov <sorganov@gmail.com>
>> ---
>>  drivers/tty/serial/imx.c | 18 ++++++------------
>>  1 file changed, 6 insertions(+), 12 deletions(-)
>> 
>> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
>> index c44a7293c013..be00362b8b67 100644
>> --- a/drivers/tty/serial/imx.c
>> +++ b/drivers/tty/serial/imx.c
>> @@ -892,27 +892,21 @@ static irqreturn_t __imx_uart_rxint(int irq, void *dev_id)
>>  	struct tty_port *port = &sport->port.state->port;
>>  	u32 usr2;
>>  
>> -	usr2 = imx_uart_readl(sport, USR2);
>> -
>>  	/* If we received something, check for 0xff flood */
>> +	usr2 = imx_uart_readl(sport, USR2);
>
> Please just place the read into the correct place in 2/8 rather than 
> moving it needlessly here again.

Well, this I considered and rejected already, before publishing the
patches.

In 2/8 this read was an initialization for the entire FIFO reading loop,
the value being re-used for flood check at the beginning as well, and
with this patch it becomes just a local read for subsequent 2 lines of
code that perform flood check, not used in the FIFO loop anymore, so I
moved it in this patch to where it now belongs.

Thanks,
-- Sergey Organov